This invention relates to a novel surgical device scalable to small dimensions for thermally-mediated treatments or thermoplasties of targeted tissue volumes. An exemplary embodiment is adapted for fusing, sealing or welding tissue. The instrument and technique utilizes electrical energy to instantly convert a biocompatible fluid media to a superheated media, perhaps a gas media, within an electrically insulated instrument working end. The altered media is characterized by a (i) a high heat content, and (ii) a high exit velocity from the working end, both of which characteristics are controlled to hydrate tissue and at the same time denature proteins to fuse, seal, weld or cause any other thermally-mediated treatment of an engaged tissue volume—while causing limited collateral thermal damage and while totally eliminating electrical current flow the engaged tissue volume.
Laser and Rf energy applications cause thermal effects in tissue based on different principles. In general, the non-linear or non-uniform characteristics of tissue affect both laser and Rf energy distributions in tissue. For example, FIG. 1A shows a typical pattern of energy distribution and resultant thermal effects in a prior art laser irradiation of tissue. The cross-section of the energy emitter or emission is indicated at ee at the tissue interface wherein a fiber optic interfaces tissue of a light beam strikes the tissue. In the case of a suitable infrared laser emission, water in tissue comprises a chromophore to absorb photonic energy resulting in a thermal effect. The turbidity of tissue scatters photons, and the resulting thermal effect is indicated by arbitrary isotherms 100, 80 and 60 which for example indicate degrees in centigrade. FIG. 1A shows that tissue desiccation d at the surface will occur to prevent photon transmission after a certain interval of energy delivery. If the objective of the thermal therapy in FIG. 1A were to seal or weld tissue, which is assumed to require a threshold temperature of 80° C., it can be seen that deeper tissue indicated at b may not reach the threshold welding temperature before the tissue surface is desiccated. Further, it can be seen that collateral tissue indicated at c may be sealed or welded, even though such tissue is collateral to the cross-section of the energy emission ee.
FIG. 1B next shows a typical energy distribution pattern when using a prior art bi-polar Rf energy delivery. In this schematic illustration, the cross-section of the energy emitter is again indicated at ee which defines the interface between a tissue surface and the electrodes 4a and 4b. As the electrodes are energized from an electrical source, the current flows are in constant flux and flow through random paths of least resistant between the electrodes. The tissue is elevated in temperature by it resistance to current flow, resulting typically in tissue desiccation or charring d at the electrode-tissue interface. When tissue in contact with the electrode is entirely desiccated, the current flow between the electrodes terminates. As represented in FIG. 1B, thermal effects typically occur in regions of tissue (indicated at c) collateral to the targeted tissue between the electrodes. Further, the prior art Rf energy delivery of FIG. 1B causes stray Rf flow in collateral tissues that may be undesirable.
What is needed is an instrument and technique (i) that can controllably deliver thermal energy to non-uniform tissue volumes; (i) that can weld tissue without desiccation or charring of surface tissue layers; (iii) that can weld a targeted tissue volume while preventing collateral thermal damage; and (iv) that does not cause stray Rf current flow in tissue.
This invention additionally relates to the working end of a medical instrument that applies energy to tissue from a fluid within a microfluidic tissue-engaging surface fabricated by soft lithography means together with optional superlattice cooling means that allows for very precise control of energy application, for example in neurosurgery applications.
Various types of radiofrequency (Rf) and laser surgical instruments have been developed for delivering thermal energy to tissue, for example to cause hemostasis, to weld tissue or to cause a thermoplastic remodeling of tissue. While such prior art forms of energy delivery work well for some applications, Rf and laser energy typically cannot cause highly “controlled” and “localized” thermal effects that are desirable in microsurgeries or other precision surgeries. In general, the non-linear or non-uniform characteristics of tissue affect both laser and Rf energy distributions in tissue. The objective of sealing or welding tissue requires means for elevating the tissue temperature uniformly throughout a targeted site.
What is needed is an instrument and technique (i) that can controllably deliver thermal energy to non-uniform tissue volumes; (i) that can shrink, seal, weld or create lesions in selected tissue volumes without desiccation or charring of adjacent tissues; (iii); and (iv) that does not cause stray electrical current flow in tissue.